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Pulsed plasma laser idea

  1. Nov 4, 2003 #1
    if i used existing laser focusing tube, with lens and everything, and i drill two holes inside a tube, parallel to each other with conductors inside them so they make a spark gap, and discharge 320 kV inside it, would light that is emitted from air plasma be sufficient to make nice beam?

    few details : i could use four 25kV capacitors connected to voltage multiplier stage as source for highvoltage pulse. laser pulse time would be somewhat equal to capacitor charge time. maybe low-pass frequency filter to make the spark brighter. and yeah, spark would be 1 cm long, and breakdown treshold for air to become plasmatic is 32 kV/cm. so i would have 10 times more voltage, thus plasma pulse would be really bright and powerfull.
  2. jcsd
  3. Nov 4, 2003 #2


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    With out fully understanding your post, I think the answer is a resounding, No.
  4. Nov 4, 2003 #3
    would you care to explain why?

    and i dont see what's non-understandable. focusing system is normal laser tube, but instead of using excited gas as source of photons, i would use big bright plasma arc that is generated when air breaks up due to intense electric field between spark gaps. air breakdown threshold is 3.2kv/mm, and my system would use ~ 32kv/mm. and then, of course, there could be more then one spark gap inside the tube, as you can apply voltage from the same source to each of them.

    as for standard laser operation, el. field is applied to excite the energy states in gas inside the tube, so they emmit photons. those photons triger a chain reaction, so more are emmited and those bunch is focused via lens to form coherent narrow beam of light.

    in "my" theoretical system, strong electric field would ionize air inside the tube, changing it's energy state to full excited plasma, photons are emitted, and chain reaction is there. not so different after all.

    so as i see it, it isn't a question will it work, it is a question of output energy.
  5. Nov 4, 2003 #4
    I'm no expert in plasma physics, but the generation of a laser beam is a little more complicated than just producing photons in a cavity. Those photons are all generated from excited atoms in identical energy states, so that the photons themselves are all exactly the same wavelength, producing a highly coherent beam of light. I'm not sure that photons created from your arc would be any more than random wavelength photons. As well, I don't see how the emitted photons would sustain any sort of chain reaction, since you require the air to be ionized in order to allow transitions.
  6. Nov 4, 2003 #5
    it's rather long now to describe whole process of corona ionization, but let's just say that ionized part of air is nitrogen, not oxygen. at atmospheric pressure paschen's law states that discharge arc is coherent, because OH radicals are dragged towards the cathode pole of spark together with all "other" molecules present in air besides oxygen and nitrogen. in a sense, you are exciting nitrogen atoms.

    ever seen an arc genereted by marx generator with lowpass filter connected to molybdenum electrodes with 10 cm spark gap? the plasma light is almost beamlike and it's brightness is same on all parts. that means that ionization effect produced 90% of photons with same wavelenght...
  7. Nov 4, 2003 #6


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    To create the population inversion required for lasing to occur requires photons of the correct energy, it is not how many photon but what frequency that matters. Your arc simply will not produce the enough of the correct photons and to many incorrect photons.

    So the answers remains simply, No. You cannot create a laser beam by smacking a laser tube with an optical sledge hammer.
  8. Nov 5, 2003 #7
    At least you can have a beautifull lantern.
  9. Nov 5, 2003 #8
    i know very well how laser operates, and i think that i can produce same frequency photons from the plasma arc. anyways i'll do some calculations and post again if i get to something.
  10. Nov 5, 2003 #9


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    The first lasers were based on flash tubes. So that is nothing new to lasers. If you match your lasing medium and the frequency of the flash tube, yes, you will produce a LASER beam. However, you simply cannot grab any old laser tube and flash it with a bright pulse of light and expect to get a LASER beam. If you do understand LASERS then I should not have to say that.

    To be specific, a Coherent AVIA Is pumped by a infra red Diode Laser, to peak power out you must set the pumping diodes output frequency precisily to match a key transition in the main crystals.

    So if you have a Lasing medium tuned to the peak frequency of your Flash tube you will get a pulsed beam, if your medium is not tuned to the Flash tube you can dump all the power you want into the meduim, it will not produce a beam.
  11. Nov 5, 2003 #10
    i was thinking to use existing nitrogen laser tube for my thing. after all, nitrogen atoms emmit photons here too. i have whole specifications on the tube, and using lens' optical characteristics i would tune plasma pulse. i can make a mathematical model of the system and tune the photon emission by changing voltage, and parameters of both conductor and cone-isolator.

    however, your way might be better. thing is i have 80% of parts needed for pulsed power supply, and i could get my hands on nitrogen tube pretty cheap. on the other hand, if i tune the system for best preformace regarding power output, i would need to order custom optical parts, witch aren't cheap at all.

    anyways Integral, thank you for your reply.
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